1. Field of the Invention
The present invention relates to a method for producing a multilayer molded article in which an skin material having nap on the outer surface, such as a fabric skin material, is attached on the outer surface of a substrate made of synthetic resin.
2. Description of the Related Art
A multilayer molded article that includes a fabric skin material attached thereon is widely used, for example, as an automobile interior component (such as in door trim or on an instrument panel) or as an component mounted on the exterior or in the interior of home electrical appliances.
As a method for producing such a multilayer molded article, a method is known in which, for example, molten thermoplastic resin is supplied to a mold comprising a pair of male and female mold halves after a fabric skin material is placed therein and the mold is held at a predetermined clamping pressure, so that the molten thermoplastic resin is molded into a predetermined configuration and that, at the same time, the fabric skin material is attached on the outer surface of the molded resin. This method offers the advantage that the fabric skin material is attached on the outer surface of the substrate made of thermoplastic resin simultaneously with the molding of the substrate, but the problem exists that the fabric skin material becomes flattened due to the clamping pressure, and the esthetic appeal (i.e., the appearance, feel, etc.) of the resulted article is compromised.
Accordingly, as a method to eliminate the loss in esthetic appeal due to the flattening of the fabric skin material in this fashion, a method has been proposed in which the mold is opened slightly after a clamping and primary cooling step, thereby forming a gap between the outer surface of the fabric skin material and the molding surface of the mold, and this condition is maintained while the thermoplastic resin undergoes secondary cooling (Japanese Patent Laid-Open No. 10-58485, Japanese Patent Laid-Open No. 11-314227). Using this method, a recovery space for the flattened nap on the outer surface of the fabric skin material is maintained, such that the previously flattened nap rises during secondary cooling, enabling a molded article that exhibits little flattening to be obtained.
However, even using this method, there remain the problems that a molded article having a good appearance is not always obtained because sufficient recovery of the flattened nap does not always occur, and that deformation sometimes occurs in the molded article due to inadequate cooling.
Accordingly, an object of the present invention is to provide a method for producing a multilayer molded article in which a fabric skin material is integrally molded with a synthetic resin substrate using a mold comprising a pair of male and female mold halves, wherein the loss in the appearance and feel due to the flattening of the fabric skin material is reliably prevented and deformation of the molded article is prevented as well.
The present invention is a method for producing a multilayer molded article in which an skin material having nap on the outer surface thereof is integrally molded with a synthetic resin substrate using a mold comprising a pair of male and female mold halves that can be moved toward and away from each other, wherein such method includes a first step of supplying a skin material to the gap between the pair of male and female halves of the mold while they are in an opened state, a second step of supplying molten synthetic resin between the back surface of the skin material and the molding surface of one of the pair of male and female mold halves that faces such back surface, a third step of clamping the mold either after the thermoplastic resin has been supplied or while it is being supplied, a fourth step of carrying out primary cooling of the molten synthetic resin while the mold is being clamped under a predetermined clamping pressure, a fifth step of opening the mold halfway and forming a predetermined gap between the pair of male and female mold halves, a sixth step of carrying out secondary cooling of the molten synthetic resin while the mold is being held in this half-open state, and a seventh step of opening the mold after the molten synthetic resin has hardened and extracting a molded article as a final product.
According to one aspect of the present invention, the time period of the operation of the fifth step to open the mold halfway is set at one second or less.
In other words, if the time period for the operation of the fifth step in which the mold is opened halfway exceeds one second, the nap tends to stay flattened during the half-opening operation, and the rising of the nap during the sixth step in which secondary cooling is performed does not take place completely, but if the half-opening step is carried out in a short interval of one second or less, the nap recovers its shape in a reliable fashion without acquiring the tendency to stay flattened. Furthermore, because the time period between the fourth step, i.e., the primary cooling step, and the sixth step is no more than one second, problems such as inadequate cooling of the molten synthetic resin do not occur. Here, the time period for the half-opening operation is the time period from the beginning of the reduction in the mold clamping pressure to the point at which the mold is halfway open.
In another aspect of the present invention, the gap formed between the pair of male and female mold halves in the fifth step is determined by adjusting in increments of 0.1 mm to ensure that the color of the outer surface of the skin material does not change significantly after molding, as well as to ensure that there is minimal deformation during molding.
The hue of the coloring of the outer surface of the fabric skin material may change due to the degree of flattening nap. Consequently, where the change in the color of the fabric skin material after molding is the smallest, the state of the nap after molding is close to the state of the nap before molding, in which there is a minimum amount of flattening. This is due to the fact that, because the pressure applied by the surface of the mold on the outer surface of the fabric skin material is reduced as the half-opening gap widens and the rising of the nap that was flattened takes place in a more reliable fashion in the sixth (secondary cooling) step, the change in the color of the outer surface of the fabric skin material after molding becomes small. On the other hand, if the half-opening gap becomes too wide, the cooling of the molten thermoplastic resin in the secondary cooling step becomes insufficient and deformation of the molded article can easily occur. Accordingly, by setting the size of the half-opening gap such that the change in the color of the outer surface of the fabric skin material after molding is small and there is minimal deformation in the molded article, insufficiency of cooling of the molten thermoplastic resin is prevented during the second cooling step and the optimal amount of recovery of the flattened nap on the outer surface of the fabric skin material is obtained. Moreover, by adjusting the gap in minute increments of 0.1 mm, the optimal size of the half-opening gap in order to obtain a molded article exhibiting the least amount of flattening and deformation can be reliably determined.
Furthermore, the present invention comprises a method for producing a multilayer molded article by integrally molding an skin material having nap on the outer surface thereof and a synthetic resin substrate using a mold comprising a pair of male and female mold halves that can come into contact with or move away from each other, wherein one of the mold halves has a movable block that is located such that it can be moved closer to or farther away from the other mold half, and the surface of the movable block facing the other mold half comprises part of the molding surface of such one mold half, and wherein such method includes a first step of supplying a skin material to a gap between the pair of male and female mold halves while the mold is in an open state and positioning the skin material such that it faces the movable block surface described above, a second step of supplying molten synthetic resin to the gap between the back surface of the skin material and the molding surface of the other mold half that faces such back surface, a third step of clamping the mold either after the molten synthetic resin has been supplied or while the molten synthetic resin is being supplied, a fourth step of carrying out primary cooling of the molten synthetic resin while the mold is being clamped under a predetermined clamping pressure, a fifth step of moving the movable block away from the other mold half and forming a predetermined gap between the movable block and the other mold half, a sixth step of carrying out secondary cooling of the molten synthetic resin while the mold is being held in the ending state of the fifth step, and a seventh step of opening the mold after the molten synthetic resin has hardened and extracting a molded article as a final product.
In this method, in another aspect of the present invention, the time period for moving the movable block in the fifth step is one second or less.
Using this method, by setting the time period for the moving of the movable block to a short interval of one second or less, the nap can be reliably restored without it acquiring the tendency to stay flattened. Furthermore, because the time period between the fourth step, i.e., the primary cooling step, and the sixth step is no more than one second, problems such as inadequate cooling of the molten synthetic resin do not occur.
In another aspect of the present invention, the gap formed between the movable block and the other mold half in the fifth step is adjusted and determined in increments of 0.1 mm to ensure that the color of the outer surface of the skin material does not change significantly after molding, as well as to ensure that there is minimal deformation.
Using this method, because the gap between the movable block after it is moved and the other mold half has the optimal size, the nap can be reliably restored and problems such as inadequate cooling of the molten synthetic resin can be prevented.
It is preferred that the gap between the pair of male and female pair of mold halves in the half-opening step, or the gap between the movable block and the other mold half in the movable block movement step, be set to 80% or more of the thickness of the final product. If the gap is less than 80% of such thickness, the pressure applied to the outer surface of the fabric skin material becomes large and the flattened nap may not be restored uniformly, and if the gap exceeds 100% of the thickness of the final product, there is insufficient cooling of the molten synthetic resin during secondary cooling. Here, the thickness of the final product is the sum of the preset thickness of the synthetic resin substrate and the thickness of the skin material before molding.
Furthermore, it is preferred that the fourth step, i.e., the primary cooling step, be divided into a first stage and a second stage, and that the mold be held at a first clamping pressure in the first stage and at a second clamping pressure that is smaller than the first clamping pressure in the second stage. The reason for this is that, if during the second stage of the primary cooling step the pressure applied to the outer surface of the fabric skin material is reduced relative to the pressure applied during the first stage, the tendency of the nap to stay flattened is mitigated. As a result, the flattened nap can be reliably restored during the subsequent second cooling step period. Moreover, because the mold comprising a pair of male and female mold halves is held at the second clamping pressure in the second stage as well, the problem of inadequate cooling of the molten synthetic resin does not occur during primary cooling, and there is no deformation of the obtained molded article.
These and other features and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described an illustrative embodiment of the invention.